A 120dB SNDR audio sigma-delta modulator with an asynchronous SAR quantizer

This paper presents a single loop 3^rd order 5-bit audio ΣΔ modulator with feed forward path. Feed forward technology relaxes the amplifier design requirement by reducing output swing of the integrators. Chopper stabilization technology is employed to mitigate the flicker noise introduced by 1^st integrator. A kind of asynchronous successive approximation (SAR) quantizer without extra fast clock replaces the traditional flash quantizer. Two voltage reference buffers are integrated on this chip as the input stages of V_refp and V_CMO to simplify off-chip circuits. Simulation results show that the modulator achieves 120dB SNDR under 5 kHz input signal within 20Hz~24kHz bandwidth. The modulator alone consumes only 20mW and the overall power consumption is less than 60mW from 3.3V supply. The active core area is 2.3×1 mm² fabricated in 0.18μm standard CMOS.